The present invention relates generally to an apparatus used in performing tests to determine the ductility of welds. Specifically, the test is carried out using the apparatus to operate upon a metallic weld test specimen by subjecting the specimen, in the vicinity of the weld, to a bending force.
It is frequently desirable or necessary to test the ductility of a weld joining two pieces of similar or dissimilar metallic materials. For example, as a product is being designed that will require welding for its assembly, the charateristics and performance of particular materials and welding techniques may be tested to ensure that they possess adequate ductility in conformance with applicable codes or standards. Failure to possess such ductility may result in a weld which can fracture when subjected to stresses or strains. As another example, training an individual in welding techniques or determining the individual's welding skill can be facilitated by testing the ductility of welds made.
The guided bend test has been widely used in the welding industry for the purposes noted above. A number of professional societies, such as the American Society of Mechanical Engineers, have defined standards for the uniform application of this test. In performing the test, a sample is made by welding two plates or two lengths of pipe together in end-to-end fashion. Single bar specimens are cut from the sample in such a way that the weld is either transverse or longitudinal to the length of the specimen. Each test specimen is supported at two points, with the weld positioned equidistantly between the support points. A ram having a curved working surface is moved into contact with the specimen at the weld, and is forced against the specimen, causing it to bend. The extent to which the specimen may be bent without breaking along the weld is indicative of the weld ductility. The presence of defects in the weld may also be exhibited by such a bend test.
A known test device for performing the guided bend test is shown in U.S. Pat. No. 3,500,679 issued Mar. 17, 1970 to Smith. The device includes a base having means for supporting the specimen at either end with the weld left unsupported. A hydraulic jack is mounted on the base, with a ram having a curved working surface being located for upward movement against the weld. A pair of rollers are positioned to be located above the specimen, so that the ram forces the specimen against the rollers in a manner that bends the specimen to drive it between the rollers.
The Smith device posesses several disadvantages. The lifting motion of the ram against the specimen from beneath the specimen causes difficulties in balancing the specimen such that bending force can be evenly applied. Further, the Smith device is relatively lightweight, making it inadequate for larger specimens.
A further problem experienced with apparatus such as the Smith device is slippage of the specimen about the ram periphery. This may occur if the thickness of the weld is different from that of the base metal or the weld metal is less ductile than the base metal. Slippage can also occur if the specimens are relatively thin.
Bend testing is not usually a continuous operation, and is normally performed only occasionally. Most manufacturing, fabricating and testing companies already own powered actuating equipment which could be used to provide the motive power needed to perform bend tests. Moreover, many smaller shops which rely upon welding would be benefited by possessing the necessary apparatus to carry out the guided bend weld test. However, because the test device represents an additional piece of powered, operating equipment, it is financially difficult for many of these establishments to justify the acquisition of such a piece of equipment. Consequently, the test must either be done without or performed by an outside contractor.
What is needed, therefore, is an apparatus for use in bend testing which is portable and capable of operating in conjunction with existing power equipment, e.g., hydraulic shop presses or tensile testing machines, which are intended for multipurpose use. The apparatus should include a means of support for the specimen which will aid in alignment and centering of the weld with respect to the ram. Further, the apparatus must be capable of handling specimens of varying sizes. The apparatus must also include means for solving the problem of specimen slippage around the ram. Such an apparatus will enable many more establishments to have access to the necessary equipment for performing bend testing. Moreover, despite relatively inexpensive construction, the apparatus must be sufficiently rugged to withstand the forces generated during performance of the test.